[CVE-2026-53089][MODERATE 7.0] bpf: Fix use-after-free in offloaded map/prog info fill [ Upstream

[CVE-2026-53089][MODERATE 7.0] bpf: Fix use-after-free in offloaded map/prog info fill [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53089
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Fix use-after-free in offloaded map/prog info fill [ Upstream
Commit: a51e7fbe94a87e236631a83973d4f558310b2cd2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a51e7fbe94a87e236631a83973d4f558310b2cd2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53089
Analysis date: Fri, 26 Jun 2026 14:06:29 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in BPF offload info reporting can increment a zero network namespace refcount during netns teardown, causing a use-after-free condition that is realistically a local DoS and may warrant Important-level review due to kernel lifetime corruption.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-53089 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53089

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-53089	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in BPF offload info reporting can occur when bpf_prog_offload_info_fill_ns or bpf_map_offload_info_fill_ns obtains the network namespace from an offload netdev while that namespace is being destroyed. The netdev pointer can remain valid under rtnl_lock and bpf_devs_lock, but the netns refcount may already be zero, so get_net can attempt to increment a zero refcount and hit a use-after-free condition. For the CVSS the PR:L is used for the paranoid score because reliable triggering may be possible for a local actor with delegated BPF or network administration capability, a service account, container root, or access to relevant offloaded BPF objects, even though typical creation of such objects is privileged. The issue is not directly network reachable and requires local interaction with BPF offload info paths plus a netns teardown race. Impact is at least local denial of service via refcount warning or kernel crash and in worst case may allow confidentiality or integrity impact due to kernel lifetime corruption, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6) 	MAYBE	BPF UAF HARDWARE  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. The commit explicitly identifies a use-after-free condition caused by `get_net()` incrementing a netns refcount that may already be zero.
* Real lifetime corruption: +1. This is a network namespace lifetime/refcount race during teardown.
* Reliable kernel crash / strong DoS: +1. The observed failure is `refcount_t: addition on 0; use-after-free`, which can become a warning, crash, or panic depending on kernel settings.
* Local high-control kernel data-plane API: +1. The path is reached through BPF object info queries, although specifically for offloaded BPF objects.
* Hard or unreliable race: -1. Triggering requires racing BPF offload info retrieval with network namespace destruction.
* Requires admin/root/CAP_* in typical deployments: -2. Creating and managing offloaded BPF programs/maps and associated netdev state is typically privileged.
* Rare AND difficult-to-reach subsystem/configuration: -1. BPF offload requires suitable hardware/driver support and offloaded objects.

Paranoid additional/adjusted signals:

* Local unprivileged or reduced-privilege trigger concern: +1. In delegated environments, container root, service accounts, or processes with limited BPF/network capabilities may interact with relevant BPF/offload objects without full host-root equivalence.
* Privilege escalation plausible, weak-to-moderate concern: +1. The primitive is a real lifetime/refcount UAF candidate, but no reliable reclaim or object-control primitive is shown.
* Confidentiality impact plausible: +1. Paranoid only, based on possible kernel lifetime corruption.
* Integrity impact plausible: +1. Paranoid only, based on possible UAF consequences.
* Availability impact realistic: +1. Host crash or panic is realistic if the refcount warning is fatal or if the stale lifetime state is later used.

## 3. Reachability analysis

The bug is local, not network reachable. It is triggered by querying info for an offloaded BPF map or program while the associated netdev network namespace is being destroyed. Typical triggering requires privileged BPF offload setup, suitable NIC/driver support, and netns teardown timing.

Namespaces and containers matter because reduced-capability root, delegated `CAP_BPF`, delegated `CAP_NET_ADMIN`, or access to preexisting offloaded BPF object file descriptors may lower the practical privilege barrier compared with full host root. However, this is not a default broadly exposed path on ordinary systems because BPF offload is hardware and configuration dependent.

## 4. Severity interpretation

This is not an ordinary cleanup bug. It is a real kernel lifetime/refcount race where `get_net()` can operate on a netns whose refcount reached zero. Realistically, the demonstrated impact is local DoS via warning/crash/panic under a hard race and uncommon BPF offload conditions.

The theoretical risk is higher because the bug class is UAF/lifetime corruption in kernel namespace management. The patch does not show a controlled reclaim, arbitrary write, or reliable object confusion primitive, so Important classification is not guaranteed. Still, the lifetime corruption and possible reduced-privilege BPF/offload reachability make it an Actionable Moderate at minimum and a Strong Important candidate for manual review.

## 5. One-sentence report phrase

A race in BPF offload info reporting can increment a zero network namespace refcount during netns teardown, causing a use-after-free condition that is realistically a local DoS and may warrant Important-level review due to kernel lifetime corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

This should not be auto-closed because it is a real UAF/refcount lifetime bug in BPF offload namespace handling, with possible reduced-privilege reachability in delegated BPF or network-admin environments.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: bpf: Fix use-after-free in offloaded map/prog info fill [ Upstream
Commit: a51e7fbe94a87e236631a83973d4f558310b2cd2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a51e7fbe94a87e236631a83973d4f558310b2cd2

Changed files:
  kernel/bpf/offload.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a51e7fbe94a87e236631a83973d4f558310b2cd2

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-53089 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53089

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 7

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).